Try vinegar. Works with PVA and other plastic wood glues. Repeatedly painting on fresh vinegar over the glue line should eventually soften it, allowing some scraping away or prying to allow more vinegar penetration. Unfortunately if the glued area is very deep this can be impossible, but you can always try anyway. Neutralizing the acidity with some hydrogen peroxide then thoroughly rinsing in water is a good idea if the wood is nice and you want to minimize discolouration and structural degradation.
Other than that I suppose you could try gently heating it through, with a hot air gun, trying to make sure you don't overheat and burn the wood. Can't un-burn wood. But if heated sufficiently all the way through, the glue could become soft enough to just pull it apart, and then scrape, carve, whatever you need to do to get rid of it and glue the thing together properly.